Despite the immense utility of DDT 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane as an insecticide, its usefulness is prejudiced by its environmental stability and low degree of biodegradability. There is growing concern about the continuing liberation of vast quantities of DDT into the environment. The very qualities which make DDT such an effective contact or residual insecticide (its stability, very low water solubility and high lipid solubility) result in its accumulation in the fatty or lipid tissues of animals and are responsible for its ecological manification in carnivorous animals at the upper ends of food chains. The problems of the biological accumulation of DDT are intensified by its enzymatic metabolic conversion to the even more stable dehydrochlorination product, DDE, 1,1-dichloro-2,2-bis-(p-chloro-phyenyl)ethylene, which is a major environmental pollutant.
The drug metabolizing or multifunction oxidase (MFO) enzymes are known to play a dominant role in determining the absolute toxicity of insecticides to both insects and higher animals. DDT and its metabolic derivatives DDE and DDD (or TDE), 1,1-dichloro 2,2-bis-(p-chlorophenyl) ethane are all highly resistant to detoxication by MFO enzymes and this single factor accounts for their storage and accumulation in animal tissues, especially at the higher ends of food chains. On the other hand, certain known symmetrical DDT analogues such as methoxychlor, 1,1,1-trichloro-2,2-bis-(p methoxyphenyl)ethane and methiochlor, 1,1,1-trichloro-2,2-bis-(p methiophenyl)ethane, are readily attacked by MFO enzymes which metabolically convert or biodegrade such analogues, into environmentally acceptable products, rapidly eliminated by animals. Thus, methoxychlor is an example of a persistent but biodegradable insecticide which does not generally accumulate in animal tissues and is a more prudent choice than DDT for a variety of uses where environmental pollution is an important factor. However, methoxychlor and other known symmetrical DDT analogues (e.g., methylchor, 1,1,1-trichloro-2,2-bis (p methylphenyl)ethane or methiochlor) while exhibiting satisfactory insecticidal activity toward certain species of insects, exhibit considerably less insecticidal activity than DDT towards other species of insects. Thus, there exists a need for improved, persistent insecticides which manifest insecticidal activity levels about comparable to DDT, but which can also be metabolically biodegraded so as to prevent their accumulation in animals, particularily vertebrata, e.g. birds, fish and mammals.